package javax.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.util.regex.Pattern;
import java.util.regex.PatternSyntaxException;
import javax.annotation.meta.TypeQualifierNickname;
import javax.annotation.meta.TypeQualifierValidator;
import javax.annotation.meta.When;

/** This qualifier is used to denote String values that should be a Regular expression. */
@Documented
@Syntax("RegEx")
@TypeQualifierNickname
@Retention(RetentionPolicy.RUNTIME)
public @interface RegEx {
  When when() default When.ALWAYS;

  static class Checker implements TypeQualifierValidator<RegEx> {

    public When forConstantValue(RegEx annotation, Object value) {
      if (!(value instanceof String)) return When.NEVER;

      try {
        Pattern.compile((String) value);
      } catch (PatternSyntaxException e) {
        return When.NEVER;
      }
      return When.ALWAYS;
    }
  }
}
